Development of a drug delivery platform using multifunctional polymeric scaffold for scar therapy

Tissue engineering is a multidisciplinary approach and has been used to promotetissue regeneration, wound repair and to enhance drug delivery. In the case of burninjury, despite the advances in treatment leading to reduced mortality, the problemof permanent, disfiguring scar formation following healing is far from beingresolved.

Scarring is the result of an imbalance of fibroblast activity resulting in an excess ofarchitecturally disorganised extracellular matrix protein deposition and ispredominantly mediated by the TGFβ pathway.

Whilst there are a number of promising therapeutic targets identified through ourincreasing understanding of scar formation, there has been limited success in theclinical translation. This can largely be attributed to difficulties with delivery,stability and efficacy of treatments tested to date.

In this thesis the problems of drug delivery and stability have been addressed using acombinatorial approach. First, a scaffold was developed to provide a platform fordrug delivery and stability. A novel multifunctional polyglycidyl methacrylate(PGMA) scaffold was developed using electrospinning. The multifunctionality ofthis polymeric scaffold was demonstrated for various applications. These includesurface functionalization of electrospun PGMA with poly (N-isopropyl acrylamide)for stimuli response surfaces and development of multifunctional nanocompositeswith (NaGdF₄:Yb, Er); Pd and Fe3O4 nanoparticles for upconversion fluorescenceimaging, sensing, and magneto-responsive properties. This was followed byexploration of modified analogues of a potential therapeutic target as anti-scarringagents. Mannose-6-phosphate (M6P) has been shown to ameliorate scarring byinhibiting the activation of TGFβ₁, a necessary step required for its receptorrecognition and function. However, therapeutic delivery of M6P to a wound iscurrently ineffective due to the low stability of M6P and limited ability to maintainM6P concentration at the site of injury. Therefore whilst targeting TGFβ activitythrough M6P has significant potential in burn therapy, stability and delivery issuesmust be addressed before this can become a therapeutic reality. Two M6P analogues, PXS25 (analogue 1) and PXS64 (analogue 2), have been developed in collaborationwith Pharmaxis Ltd., to overcome the metabolic vulnerability of M6P whilstretaining the receptor recognition function. Initial work was carried out toinvestigate the biocompatibility and cytotoxicity capabilities of both analoguescompared to M6P in human dermal skin fibroblasts. Subsequently they wereinvestigated for their proficiency in regulating the expression of the critical fibroticmarker, Collagen I. Analogue 2 was shown to significantly inhibit TGFβ₁ mediatedup-regulation of collagen I gene expression. However, the lipophilic analogue 2 haslimited bioavailability. The final chapter addresses this specific problem byincorporating analogue 2 into the multifunctional scaffold and testing the efficacy ofthe combined drug/scaffold therapy on human dermal skin fibroblasts.

The tissue engineering approach presented herein demonstrated the potential ofcombinatorial scaffold mediated drug delivery method to progress some of theexisting therapeutic targets into clinical therapies. The future work using porcinewound healing model is a necessary extension to establish the efficacy and potentialof this combinatorial approach in vivo before its clinical translation.